Pharm Chemistry
Synthesis, Characterization, and Biological Evaluation of certain 6-methyl-2(3H)-benzo-1, 3-thiazolyl-1'-ethylidene-2-(o, pSubstituted Acetophenones) Hydrazine Analogs Alang G, Kaur G, Kaur R, Singh A, Tiwari R1 G.H.G Khalsa College of Pharmacy, Gurusar Sadhar - 141 104, Punjab, 1Department of Biotechnology, Punjab University, Chandigarh, India Address for correspondence: Dr. Gaurav Alang; E-mail:
[email protected]
ABSTRACT In the present study, five new derivatives (GG4 to GG8) of benzothiazoles were synthesized and evaluated against Staphylococcus aureus (MTCC 737), Pseudomonas aeruginosa (MTCC 424), Escherichia coli (MTCC 1687), and yeast-like fungi Candida tropicalis. p-Toluidine on treatment with ammonium thiocynate formed 2-benzothiazolamines (II), which on reaction with hydrazine hydrate formed a hydrazino derivative (III). Compounds GG4 to GG8 were synthesized by reacting the hydrazine derivative with different acetophenones. All the synthesized compounds were identified by IR and 1H-NMR, and antimicrobial activity was performed on the synthesized compounds. Presence of NO2, Br, OCH3, and Cl groups to the substituted benzothiazole enhanced the antibacterial and antifungal activities. Key words: Antimicrobial activity, substituted acetophenones, 2-aminobenzothiazole DOI: 10.4103/0975-1483.71636
INTRODUCTION
‘Riluzole’ the first benzothiazole containing an antiepileptic drug is the role model for the synthesis of various compounds with different activities based on a benzothiazole moiety. Since then, significant research has been carried out taking benzothiazole as the basic moiety. From the literature survey, it has been found that extensive work has been reported on 2-substituted benzothiazole derivatives in the past and evaluated for different activities, such as, antibacterial,[1] antiproliferative activity,[2] antiviral,[3] antitumor,[4] antifungal,[5] anti-inflammatory,[6] antioxidative and radioprotective, [7] antidiabetic, [8] antihelmintic, [9] antileishmanial,[10] anticonvulsant,[11] antimycobacterial,[12] neuroprotective,[13] and antipsychotic.[14] There are a number of pharmaceuticals and nutraceutical drugs available in the 394
market containing benzothiazole moiety, reported to have different clinical uses. Phortress, [Figure 1] an antitumor drug has shown promising results in the clinical trials. Taking this into consideration, certain derivatives have been synthesized taking benzothiazole as the basic moiety. Experimental All the chemicals and solvents used during the experimental studies were of analytical grade and were procured from CDH, New Delhi and Sigma Chemicals, Mumbai. Melting points of all synthesized compounds were determined by using an open capillary tube and were uncorrected. Infrared (IR) data were recorded in KBr disks, on a Perkin Elmer R-IX FTIR spectrophotometer, and the H1 NMR spectra on Bruker AC 30 of the NMR spectrometer 400 MHz. Journal of Young Pharmacists Vol 2 / No 4
Synthesis, characterization, and biological evaluation of certain hydrazine analogs
2-Hydrazino-6-methylbenzothiazole (III)
Figure 1: Molecular model of Phortress - An anti- tumor drug
CHEMISTRY
p-Tolylthiourea (I) p-Toluidine (5.35 g) was dissolved in a mixture of concentrated HCl (4.3 ml) and water (11.6 ml) by heating in a water bath. The contents were cooled and solid ammonium thiocyanate (3.5 g) was added. The mixture was heated on water bath for about 22 hours. The precipitated product was cooled and filtered, washed with water three to four times, and dried. It was recrystallized with aqueous methanol to get cream colored crystals. Yield: 88% (m.p: 130○C). IR: 3435 (N-Hstr), 2999 (Aliphatic C-Hstr), 1612 (N-Hben), 1462 (Aromatic C=Cstr), 1310 (Aromatic C-Hben) 1H-NMR: 3.35 (2H, s, NH2), 7.24-7.11 (4H, d, Ar-H), 2.30 (3H, s, CH3). 2-Amino-6-methylbenzothiazole (II) Fifteen milliliters of concentrated H2SO4 was added to p-tolylthiourea (8.3 g) and the temperature of the mixture was raised to 800C on a water bath. Next, 48% HBr (0.5 g) acid was added slowly and the reaction mixture was stirred for two hours and set at 800C. It was then cooled to room temperature and the reaction mixture was slowly introduced to cold water and then adjusted to pH 9 or 10 by adding ammonia water. The whole mixture was stirred for one hour by heating at 700C and then cooled to room temperature. The mixture was extracted twice with dichloromethane and the combined extract was dried with anhydrous sodium sulfate and evaporated, to obtain the title compound. Yield: 80% (m.p: 145○C). IR: 3395 (N-Hstr), 3261 (N-Hstr), 1462 (Aromatic C=Cstr), 1326 (Aromatic C-Nstr), 1253 (C-Sstr). 1H-NMR: 3.45 (2H, s, NH2), 7.327.26 (3H, m, Ar-H), 2.34 (3H, s, CH3). Journal of Young Pharmacists Vol 2 / No 4
2-Amino-6-methybenzothiazole (20 g) [0.82 mmol] and hydrazine hydrate (85%) [0.11 mmol] in 50 ml of ethylene glycol were refluxed by stirring for four hours (600C). The color of the reaction changed to green and a homogeneous solution appeared. A white solid was precipitated at the end of the reflux period. The mixture was cooled and the product was filtered and then washed with water several times. It was air dried and recrystallized by using ethanol. Yield: 43% (m.p: 192○C). IR: 3434 (NHNHstr), 3162 (Aromatic C-Hstr), 3000 (Aliphatic C-Hstr), 1611.9 (N-Hben). 1H-NMR: 9.59 (1H, s, NH), 7.34-7.11 (5H, m, Ar-H), 3.37 (2H, s, NH2), 2.26 (3H, s, CH3). 2-{(3''-nitrophenyl)-1'-ethylidene}-hydrazinyl-6methylbenzo-1, 3-thiazole (GG4) 2-Hydrazino-5-methylbenzothiazole (1.5 mmol), 3-nitroacetophenone (2.2 mmol), and glacial acetic acid (2–3 drops) were taken in absolute ethanol (20 ml) and refluxed on a water bath for eight hours, till different spots appeared, on thin layer chromatography (TLC) . On cooling, the solid was separated. It was filtered and washed with little water and recrystallized with absolute ethanol. Yield: 48% (m.p: 181○C). IR: 3428 (N-Hstr), 3087.8 (Aromatic C-Hstr), 1613.9 (C=Nstr), 823 (Aromatic C-Nstr). 1H-NMR: 8.77 (1H, s, NH), 7.36-7.06 (7H, m, Ar-H), 2.38 (3H, s, CH3), 2.69 (3H, s, CH3). 2-{(4''-bromophenyl)-1'-ethylidene}-hydrazinyl-6methylbenzo-1, 3-thiazole (GG5) 2-Hydrazino -5-methylbenzothiazole (1.5 mmol), 4-bromoacetophenone (2.2 mmol), and glacial acetic acid (2–3 drops) were taken in absolute ethanol (20 ml) and refluxed on a water bath for eight hours till different spots appeared, on TLC. On cooling, the solid was separated. It was filtered and washed with little water and recrystallized with absolute ethanol. Yield: 52% (m.p: 189○C). IR: 3434 (NHstr), 3164 (Aromatic CHstr), 1612 (C=Nstr), 1581 (NHben), 699 (C-Brstr). 1H-NMR: 9.58 (1H, s, NH), 7.267.12 (7H, m, Ar-H), 2.50 (3H, s, CH3), 2.27 (3H, s, CH3). 2-{(4''-methoxyphenyl)-1'-ethylidene}-hydrazinyl-6methylbenzo-1, 3-thiazole (GG6) 2-Hydrazino-6-methylbenzothiazole (1.5 mmol), 4-Methoxyacetophenone (2.2 mmol), and glacial acetic acid (2–3 drops) were taken in absolute ethanol (20 ml) and refluxed on a water bath for eight hours till different spots appeared, on TLC. On cooling, the solid was separated. It was filtered and washed with little water and recrystallized 395
Alang , et al. J Young Pharm. 2010;2(4): 394-398 with absolute ethanol. Yield: 41% (m.p: 169○C). IR: 3435 (N-Hstr), 3165 (Aromatic C-Hstr), 1612 (C=Nstr), 1581 (N-Hben), 1285 (Aromatic C-Nstr). 1H-NMR: 9.59 (1H, s, NH), 7.25-7.11 (7H, m, Ar-H), 6.72 (1H, s, NH2), 2.97 (3H, s, CH3), 2.33 (3H, s, CH3). 2-{(2'',4''-dichlorophenyl)-1'-ethylidene}-hydrazinyl6-methylbenzo-1,3-thiazole(GG7) 2-Hydrazino-6-methylbenzothiazole (1.5 mmol), 2,4-Dichloroacetophenone (2.2 mmol), and glacial acetic acid (2–3 drops) were taken in absolute ethanol (20 ml) and refluxed on a water bath for eight hours till different spots appeared, on TLC. On cooling, the solid was separated, and was filtered and washed with little water and recrystallized with absolute ethanol. Yield: 54% (m.p: 177○C). IR: 3434 (N-Hstr), 3164 (Aromatic C-Hstr), 1612 (C=Nstr), 1582 (N-Hben), 800 (Aromatic C-Clstr). 1H-NMR: 9.59 (1H, s, NH), 7.25-7.11 (7H, m, Ar-H), 3.40 (3H, s, CH3), 2.26 (3H, s, CH3).
Staphylococcus aureus (MTCC 737), Gram negative bacteria — Pseudomonas aeruginosa (MTCC 424), Escherichia coli (MTCC 1687), and yeast-like fungi Candida tropicalis. The concentration of the test compound used was 50 mg/ml. Ampicillin and Clotrimazole were taken as the standard drugs [Tables 1 and 2]. Acetone was used as solvent control. The zone of inhibition obtained in different strains of bacteria and fungi are shown graphically in case of S. aureus [Graph 1], P. aeruginosa , E. coli [Graph 2], C. tropicalis [Graph 3], and with the help of original images taken [Figure 3], respectively.
CH3
CH3 a
NH2
b S
C
RESULTS AND DISCUSSION
S N
(II)
NH H 3C
S (III)
N
d H3C
Compounds GG4 GG5 GG6 GG7 GG8
NH2
c
NH2 (I)
2-{(2'',4''-dimethoxyphenyl)-1'-ethylidene}hydrazinyl-6-methylbenzo-1,3-thiazole(GG8) 2-Hydrazino-6-methylbenzothiazole (1.5 mmol), 2,4-Dimethoxyacetophenone (2.2 mmol), and glacial acetic acid (2–3 drops) were taken in absolute ethanol (20 ml) and refluxed on a water bath for eight hours, till different spots appeared, on TLC. On cooling, the solid was separated, and was filtered and washed with little water and recrystallized with absolute ethanol. Yield: 58% (m.p: 185○C). IR: 3433 (O-H and N-Hstr), 3163 (Aromatic C-Hstr), 1610 (C=Nstr), 1415 (Aromatic C=Cstr). 1H-NMR: 9.58 (1H, s, NH), 7.387.11 (7H, m, Ar-H), 3.38 (3H, s, OCH3), 2.26 (3H, s, CH3).
H3C
R H H H Cl OCH3
NHNH2
R'
R''
R NH N N C CH3 (GG4-GG8) S
R' NO2 H H H H
R'' H Br OCH3 Cl OCH3
Figure 2: Reagents and Conditions; (a) ammonium thiocyanate, HCl, H2O, reflux, 22 hours; (b) HBr, H2SO4, reflux, 2 hours; (c) NHNH2, ethylene glycol, reflux, 4 hours; (d) appropriate substituted acetophenones, glacial CH3COOH, EtOH
The efficient synthetic route for the synthesis of benzothiazole derivatives is shown below [Figure 2]. p-Toluidine on reacting with ammonium thiocyanate formed p-Tolylthiourea (I), which on reaction with hydrobromic acid yielded 2-benzothiazolamines (II). This on reaction with hydrazine hydrate formed hydrazino derivatives (III). The compounds (GG4 to GG8) were synthesized by reacting with hydrazine derivatives, with different acetophenones (3-nitroacetophenone, 4-bromoacetophenone, 4-methoxyacetophenone, 2, 4-dichloroacetophenone, 2, 4-dimethoxyacetophenone). Antimicrobial activity In the present study, the efficacy of five new compounds was detected against Gram positive bacteria — 396
Figure 3: 3% Zone of inhibition in different strains using the agar disk diffusion method Journal of Young Pharmacists Vol 2 / No 4
Synthesis, characterization, and biological evaluation of certain hydrazine analogs Table 1: Comparison of the zone of inhibition of various synthesized compounds
Table 2: Comparison of antimicrobial activity with different synthesized compounds
Compounds
Compounds
Standard GG4 GG5 GG6 GG7 GG8
Anti-bacterial activity S. aureus 14 mm 11 mm (78) 2 mm (14) – –
E. coli 15 mm 10 mm (66) – – –
–
–
Antifungal activity P. aeruginosa C. tropicalis 14 mm 16 mm – 11 mm (68) – 5 mm (31) – 2 mm (12) – 6 mm (37) –
–
Standard GG4 GG5 GG6 GG7 GG8
Anti-bacterial activity S. aureus +++ +++ + – –
E. coli – – – – –
–
–
Antifungal activity P. aeruginosa C. tropicalis +++ +++ – +++ – ++ – + – ++ –
–
Figures indicates in parentheses are in percentage
+++ Diameter of zone of inhibition between 11 and 16 mm, ++ Diameter of zone of inhibition between 5 and 10 mm, + Diameter of zone of inhibition between 2 and 5 mm, - No zone of inhibition observed
Graph 1: Comparison of % Zone of inhibition in case of S. aureus
Graph 2: Comparison of % Zone of inhibition in case of E. coli
From the above-mentioned results, it may be concluded that the derivatives of benzothiazoles possess moderateto-potent antimicrobial activity [1,5] when compared to the standards. Furthermore, other sites (6 and 7) available at the benzothiazole moiety would be explored, in order to obtain compounds with different activity and potent antimicrobials. Therefore, the present study will help scientists in future, to undertake a different mode to synthesize more potent antimicrobials. ACKNOWLEDGMENT
Graph 3: Comparison of % Zone of inhibition in case of C.tropicalis
Compound GG4 showed significant activity against S. aureus, E. coli, and C. tropicalis when tested at 50 mg/ml concentration taking ampicillin and clotrimazole as the standard. From the SAR studies, the presence of the electron withdrawing group (i.e., NO2) in compound GG4 was assumed to be responsible for the observed activity. Journal of Young Pharmacists Vol 2 / No 4
The authors are grateful to Mr. Avtar Singh, Punjab University, Chandigarh, and Mr. Shakeek Jamia Hamdard, Delhi, for carrying out IR and 1HNMR of the various derivatives synthesized. REFERENCES 1.
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Source of Support: Nil, Conflict of Interest: None declared.
Journal of Young Pharmacists Vol 2 / No 4
